Highly selective separation of uranium by biochar-based porous materials through sorption, precipitation, photocatalysis, and electrocatalysis strategies

The fast utilization of nuclear energy requires the preconcentration and separation of uranium (U(VI)) from different kinds of water solutions, which is crucial for the sustainable development of nuclear power plants. Efficient recovery of U(VI) from different systems through the strategies of sorption, (co)precipitation, photocatalysis, electrocatalysis, etc., has been extensively studied. Among the studied materials, biochar and biochar-based porous materials exhibit potential real applications in U(VI) selective separation from solutions because of their easy synthesis at low cost on a large scale, eco-environmental friendliness, high surface areas with abundant special functional groups for strong binding of U(VI) ions and high stability/reusability. The selective separation of U(VI) is primarily governed by ligand-specific coordination (e.g., amidoxime and phosphate groups), surface charge-dependent electrostatic interactions, and redox transformation pathways under catalytic conditions. Herein, the applications of biochar and biochar-based porous materials for efficient and selective separation of U(VI) from complex systems through different strategies are described and summarized, and the reaction mechanisms of U(VI) interaction with biochar and biochar-based materials by different techniques are discussed at the molecular level. In the end, the use of machine learning for construction and evaluation of biochar and biochar-based porous materials in highly selective extraction of U(VI) and the challenges of biochar and biochar-based porous materials in U(VI) removal in real applications are described.